[tang-vu]

Clicking Download for an existing large model now acknowledges the request promptly and reports verifying while hashing runs. Previously, synchronous verification could exceed the request deadline while Cancel reported no download. Valid files are reused; cancellation and inspection failures preserve existing artifacts. Explicit stat keeps unreadable files distinct from missing files on Python 3.14.

Closes #7402. Supersedes archived #7262.

Release Lane

• Mainline change targeting main

Changed Surface

• Dashboard API / host agent

Risk And Validation

Reviewed head: 32bed27ffd556bbca010fc570eb99cec1fc9807d. This changes model verification and lifecycle ownership.

• 621 focused backend tests and 64 frontend hook/deadline/polling tests passed; CI passed 76/76 checks. CI Ruff options and Python 3.9 syntax checks passed.
• Actual Python 3.14.3 HTTP fault injection reproduced valid-file deletion before the explicit-stat correction. The corrected implementation preserves the artifact, reports inspection failure, and releases ownership.
• Final host-agent bytes were tested on an installed Windows/WSL laptop alongside fix(models): retain cancelled download results for Retry #7467's dashboard. Real Edge controls switched 9B to 4B, started verification of the existing 5.68-GB 9B artifact, cancelled it, retried verification to completion, and switched back to 9B. Full SHA256, inode, size, mtime, mode and owner remained unchanged. The inactive-file fixture restored the original bytes before every Download request.
• The candidate overlays were removed and the original host agent/dashboard restored, with 9B active. Production bytes match the prospective combined tree on main b9b1de03; 31 combined hook tests passed.

Operational Change Check

• Focused installed-host/browser acceptance and exact-head CI passed. Complete current-main installs and journeys on all four required fleet machines remain pending.

Compatibility And Rollback

Existing-file requests return started rather than synchronous already_downloaded; polling reaches complete. Cancellation is checked between digest chunks and cannot interrupt a blocked filesystem read. Integrity checks, URL restrictions and split-part reuse remain in place. Reverting retains model files and persisted configuration.

AI Assistance

Contributor work was followed by Tower2 model review, Codex review, executed regressions and live browser testing. Automated evidence does not imply human verification.